Mammalian α-L-fucosidases (EC 3.2.1.51) are a ubiquitous group of multimeric lysosomal glycosidases involved in the degradation of a diverse collection of fucose-containing oligosaccharides, glycolipids and glycoproteins. The importance of this enzyme in mammalian metabolism is evidenced by deficiency or absence of enzymatic activity leading to the fatal genetic disease fucosidosis. Mammalian α-L-fucosidases are sialoglycoproteins and the presence and amount of sialic acid contribute to producing multiple isoforms which can differ in various species as well as in different tissues within a given species. These enzymes are closely related structurally as indicated by immunochemical cross-reactivity and cloning studies. α-L-Fucosidases have similar kinetic properties (pH optimum, K_m values) with synthetic substrates and exhibit broad substrate specificity on natural substrates. Numerous linkages (α1 -2, α1-3, α1-4, α1-6) of L-fucose, primarily to galactose and N-acetylglucosamine, can be hydrolyzed with preference shown for fucose in α1-2 linkage to galactose in low molecular-weight, water soluble compounds. Recent studies have provided evidence for a novel, plasma membrane-associated sperm fucosidase which may be involved in sperm-egg interactions and/or fertilization.